As shown in FIG. 1, FIG. 1A and 2, the conventional photo sensing device comprises at least one light source 1, a photo detector 3 and an optical chopper 2. The light source 1 is placed in the proximity of the chopper 2, therefore the light emitted from the light source 1 can impinge upon the chopper 2. The photo detector 3 is placed near the perimeter of the chopper and contains a photo sensing chip 31 to receive the work beam 11 reflected from the chopper 2. Moreover, two or four inclined planes 32 are provided on the periphery of the chip 31 to eliminate the interference of work beam 11 when impinging upon the photo detector.
The present invention is intended to provide an improved photo sensing device to further eliminate the interference of the light from light source when work beam impinges upon the photo detector.
To achieve the above object, the photo sensing device according to the present invention provides a cone-shaped surface, two inclined surfaces or four inclined surfaces on the light-impinging surface of the photo-sensing chip. Moreover, a light-absorbing material can be applied to the inclined surfaces to eliminate the interference from reflected light.